Method of making a structural member for use in the automobile industry

ABSTRACT

In a method of making a structural member for the automobile industry, a blank of boron steel is pre-formed at ambient temperature into an intermediary part of a configuration which substantially corresponds to an end shape of a finished structural member. The intermediary part is then coated with aluminum or an aluminum alloy and exposed to a temperature above the upper transformation line in the TTT curve. Subsequently, the intermediary part is formed in a mold into the finished structural member while being hardened at the same time.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the priority of German Patent Applications, Serial Nos. 102 04 969.6, filed Feb. 6, 2002, and 102 20 323.7, filed May 7, 2002, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates, in general, to a method of making a structural member for use in the automobile industry.

[0003] Structural members for the automobile industry involve, e.g., bumpers, side impact carriers or door pillars. A majority of such structural members are made from boron steel that has been coated with aluminum. The structural members are hereby made directly from a heated blank into a finished shape. However, structural members made of boron steel and coated with aluminum cannot be made by a single process step into the final configuration, when the structural members have a complex shape. In this case, the manufacture of the structural members requires a succession of cold-forming steps in two or more tools. As a consequence, the aluminum coat ruptures during the forming process so that the base material becomes exposed. The protective coating is thus destroyed.

[0004] It would therefore be desirable and advantageous to provide an improved method of making structural members for use in the automobile industry, which method obviates prior art shortcomings and which is suitable to manufacture even complex shapes of structural members.

SUMMARY OF THE INVENTION

[0005] To ensure clarity, it is necessary to establish the definition of important terms and expressions that will be used throughout this disclosure. The term “ambient temperature” is used to refer to “room temperature”. The terms “TTT curve” or “time-temperature-transformation curve” are generally known to the person skilled in the art and relate to diagrams of the transformation period of steel at different temperatures.

[0006] According to one aspect of the present invention, a method of making a structural member for use in the automobile industry, includes the steps of shaping a blank of boron steel at ambient temperature into an intermediary part of a configuration which substantially corresponds to an end shape of a finished structural member, coating the intermediary part with aluminum or an aluminum alloy, heating the intermediary part to a temperature above the upper transformation line in the TTT curve, and forming the intermediary part in a tool into the finished structural member at simultaneous hardening of the structural member.

[0007] According to another aspect of the present invention, a method of making a structural member for the automobile industry, includes the steps of shaping a blank of boron steel at ambient temperature into an intermediary part of a configuration which substantially corresponds to an end shape of a finished structural member, heating the intermediary part to a temperature above the upper transformation line in the TTT curve, coating the intermediary part in a melt with aluminum or an aluminum alloy at a temperature above the upper transformation line in the TTT curve, and forming the intermediary part in a tool into the finished structural member at simultaneous hardening of the structural member.

[0008] According to still another aspect of the present invention, a method of making a structural member for the automobile industry, includes the steps of shaping a blank of boron steel at ambient temperature into an intermediary part of a configuration which substantially corresponds to an end shape of a finished structural member, placing the intermediary part in a melt of aluminum or an aluminum alloy at a temperature above the upper transformation line in the TTT curve, coating the intermediary part in the melt, and forming the intermediary part in a tool into the finished structural member at simultaneous hardening of the structural member.

[0009] With a method according to the present invention, it is now possible to make structural members that are made of boron steel and coated with aluminum and aluminum alloy and that have a complex configuration, without damage to the coating during the shaping process.

[0010] Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

[0011] None

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0012] The described embodiments are to be understood as illustrative of the invention and not as limiting in any way.

[0013] In accordance with a first variation of the present invention, a blank of boron steel is cut from a coil and, depending on its complexity, is shaped to an intermediary part in one or more tools in succession, until the intermediary part has a shape that substantially resembles the shape of the finished structural member to be manufactured. Pre-forming of the blank of boron steel is simple hereby in view of the absence of a coating. After being shaped to the desired configuration, the intermediary part is heated to a temperature of about 650° C. and coated with aluminum or an aluminum alloy, e.g. through a dipping process.

[0014] The intermediary part, after being coated with aluminum or an aluminum alloy is then heated to a temperature above the upper transformation line in the time-temperature-transformation curve (TTT curve) and thereafter shaped in a tool into the end configuration of the structural member while being hardened at the same time. The heating temperature is about 930° C.

[0015] In accordance with a second variation of the present invention, the pre-formed intermediary part, produced by the shaping process as described in the first variation, is now heated to a temperature above the upper transformation line in the TTT curve, e.g. at a temperature of 930° C., and then coated in a melt with aluminum or an aluminum alloy at a temperature also above the upper transformation line in the TTT curve. Finally, the intermediary part is shaped in a tool into the end configuration of the structural member while being hardened at the same time.

[0016] In accordance with a third variation of the present invention, the pre-formed intermediary part is heated in an aluminum melt to a temperature above the upper transformation line in the TTT curve, e.g. at a temperature of 930° C., and then shaped in a tool into the end configuration of the structural member while being hardened at the same time.

[0017] Of course, it is certainly conceivable in all three variations of a method according to the present invention to further enhance the quality of the end product by applying an additional process step, e.g. quenching and tempering.

[0018] While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0019] What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and their equivalents: 

What is claimed is:
 1. A method of making a structural member for use in the automobile industry, comprising the steps of: shaping a blank of boron steel at ambient temperature into an intermediary part of a configuration which substantially corresponds to an end shape of a finished structural member; coating the intermediary part with aluminum or an aluminum alloy; heating the intermediary part to a temperature above the upper transformation line in a TTT curve; and forming the intermediary part in a mold into the finished structural member at simultaneous hardening of the structural member.
 2. The method of claim 1, wherein the coating step is carried out at a temperature of about 650° C.
 3. The method of claim 1, wherein the coating step is carried out in a dipping process.
 4. The method of claim 1, wherein the temperature above the upper transformation line in a TTT curve is about 930° C.
 5. A method of making a structural member for use in the automobile industry, comprising the steps of: shaping a blank of boron steel at ambient temperature into an intermediary part of a configuration which substantially corresponds an end shape of a finished structural member; heating the intermediary part to a temperature above the upper transformation line in the TTT curve; coating the intermediary part in a melt at a temperature above the upper transformation line in the TTT curve with aluminum or an aluminum alloy; and forming the intermediary part in a tool into the finished structural member at simultaneous hardening of the structural member.
 6. The method of claim 5, wherein the temperature above the upper transformation line in a TTT curve is about 930° C.
 7. A method of making a structural member for use in the automobile industry, comprising the steps of: shaping a blank of boron steel at ambient temperature into an intermediary part of a configuration which substantially corresponds an end shape of a finished structural member; placing the intermediary part in a melt of aluminum or an aluminum alloy at a temperature above the upper transformation line in the TTT curve; coating the intermediary part in the melt; and forming the intermediary part in a mold into the finished structural member at simultaneous hardening of the structural member.
 8. The method of claim 7, wherein the temperature above the upper transformation line in a TTT curve is about 930° C. 